The present invention relates generally to agricultural harvesters and, more particularly, to agricultural combine harvesters with a transverse fan assembly having a noise-reducing, flow enhancing inlet structure.
Transverse fan assemblies used in agricultural combines are well known in the art. A typical agricultural combine includes a crop header apparatus which reaps planted grain stalks and then feeds the grain stalks to a threshing apparatus arranged within a body of the combine. The threshing apparatus functions to separate grain from material other than grain. As part of the threshing process, the grain is separated to fall or exit through openings in the threshing apparatus into the cleaning apparatus while material other than grain is discharged from the combine. Transverse fan assemblies provide air flow through sieves in the cleaning apparatus to separate grain from the smaller non-grain crop material sometimes called “chaff.” Grain is collected within the combine while the chaff is discharged from the combine, partially aided by air flow from the fan assembly of the cleaning apparatus.
With the increased productivity demands on modern agricultural combines, cleaning capacity has become a limiting factor to overall harvesting performance of the combine. The most readily achieved method of increasing combine efficiency is by increasing the size of the cleaning area and the sieves to spread the crop materials across a wider area and in a thinner crop mat or veil which necessitates increased air flow through the cleaning area. Conventional methods for increasing air flow provided by a transverse fan of a given width require increasing the fan tip speed, whether by increasing the fan rotational speed, increasing fan diameter, or a combination of both. Unfortunately, these methods result in increased noise from the operating fan which increases overall noise level of the combine. Moreover, space limitations often preclude increasing fan diameter as a means to increase air flow.
One method for reducing fan noise is to provide a fan having angled blades. Transverse fans having straight blades generate considerable noise as each blade passes a straight plenum cutoff edge as the blade and the edge will be instantaneously adjacent for the entire length of the fan. Transverse fans having angled blades, such as that disclosed in U.S. Pat. No. 5,599,162, reduce noise by reducing the portion of the fan blade that passes a straight cutoff edge at any instant in time. There are limitations in the angle to which a transverse fan blade may be positioned beyond which air flow in the axial direction becomes problematic and affects air flow distribution uniformity from the fan outlet.
It would be a great advantage to provide an improved cross flow fan capable of providing increased air flow to meet the needs of higher capacity combines without increasing the operating noise level of the fan thereby overcoming the above problems and disadvantages.